Telomere length as a prognostic marker in colorectal cancer: a scoping review

Search strategy

Pubmed and Embase were systemically searched to identify studies investigating telomere length and CRC prognosis in adherence with the Preferred Reporting Items for Systematic review and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR) checklist⁶. MeSH terms including “telomere”, “colorectal neoplasms”, “colonic neoplasms”, and “rectal neoplasms” were used for Pubmed search. Emtree terms including “telomere length”, “colorectal cancer”, “colon cancer”, and “rectum cancer” were used for Embase search. Studies were selected for review if they met all of the following criteria: 1) human CRC cancer patients were included; 2) telomere length from a tissue sample or from blood sample was measured; 3) clinical outcomes were reported as survival rate or disease relapse. The latest search was performed on April 22, 2019. No date limits were imposed and there was no language limitation.

Review of studies

Two researchers (G.K. and K.Y.L.) reviewed all included studies and extracted the following data independently: author, year, country, origin of samples, cancer site, sample size, mean (or median) age of involved patients, tumor stage, assay or detection method for telomere length, follow up period, and survival outcome. A pilot test for three articles to check the data extraction form and to ensure consistency was performed before data extraction.

A detailed review protocol is available as Extended data⁷.

Studies identified

In total, 533 studies were initially screened from Pubmed database and 815 studies were screened from Embase. Among 1,348 studies, 1,336 studies were excluded and 12 studies were finally identified to report the association between telomere length and prognosis of CRC between 2004 and 2019. The included cases from 12 studies were 1,955. Of these studies, ten measured telomere length from tissue samples (Table 1) and two measured telomere length from peripheral leukocytes (Table 2). There were seven studies from Europe, three from Asia, one from the USA, and one from Australia.

Studies finding associations between telomere length and CRC prognosis

In brief, the results from 12 studies are contradictory. First, two of ten studies analyzing tissue samples showed better prognosis of patients with longer telomere length, especially in patients with metastasis^8,9.

Balc’h et al. measured telomere length from 125 CRC tissue samples⁸. A significant shortening of telomere length in the tumor tissue compared with the normal tissue was observed. They reported that the overall survival rate was significantly correlated with telomere length in metastatic disease (n=28, p=0.03). In metastatic disease, patients with longer telomeres survived longer than those with shortened telomeres. However, there was no statistically significant difference in overall survival rate between the maintained telomere length group and shortened telomere length group when analyzing localized disease group (n=97) or the entire group (n=125). In addition, they observed that telomere length was significantly associated with the occurrence of mutation in KRAS. They found that the shorter the telomeres in healthy tissue were, the longer the telomeres in tumor tissue were. They suggested that telomere length in healthy normal tissue might influence telomere maintenance mechanisms in a tumor.

Augustine et al. measured telomere length from 75 CRC tissue samples and explored the efficacy of telomere length as a predictor for response to anti-TGFR therapy in metastatic disease⁹. They first measured telomere length in 21 human-derived CRC cell lines. When the cell lines were treated with cetuximab, a monoclonal antibody to EGFR, growth of cell lines with a longer telomere length was inhibited to a significantly larger degree than cell lines with a shorter telomere length (p=0.02). When the analysis was limited to K-ras wild-type cell lines only, growth of cells with a longer telomere length was more inhibited by cetuximab treatment compared with cells with a shorter telomere length (p=0.04), which was similar to above. Next, they analyzed telomere length in patients’ tumor samples. In the analysis of all human CRC samples, progression-free survival after anti-EGFR therapy was significantly longer in patients with longer telomere length compared with that of patients with shorter telomere length (n=75, p=0.026). Furthermore, when the analysis was narrowed down to the patients with K-ras wild-type tumors only, again, patients with longer telomere length showed longer progression-free survival than patients with shorter telomere length (n=43, p=0.012). The authors suggested that telomere length could play a role as a marker for predicting the benefit of anti-EGFR treatment in metastatic CRC.

The two aforementioned studies suggested the telomere length as a prognostic marker in metastatic CRC^8,9. The longer the telomere, the better the prognosis was. On the contrary, the next four studies among the ten to examine tissue samples showed better prognosis of patients with shorter telomere length^10–13.

Fernández-Marcelo et al. analyzed 132 CRC tissue samples and corresponding noncancerous normal tissue samples, and measured telomere length, a ratio of telomere length in cancer to normal tissue (TL ratio), and telomerase activity¹⁰. Patients with shorter telomere length showed a significantly longer disease-free survival compared with those with longer telomere length (p<0.001). Moreover, patients with the lowest TL ratio never experienced recurrence during the follow-up period (median 60 months, p=0.043). Cox multivariate analysis also showed that mean telomere length was an independent prognostic factor for disease-free survival (p=0.017). The authors suggested the use of telomere status as an independent prognostic factor.

Valls et al. analyzed 147 CRC tissue samples and paired normal tissue samples. The authors measured the telomere length of the samples and calculated the TL ratio, which is defined as a ratio of telomere length in cancer to normal tissue¹¹. Univariate analysis and multivariate Cox regression analysis both showed a significant relationship between TL ratio and overall survival rate. Patients with lower TL ratios exhibited a significantly longer overall survival rate (n=125, p=0.014). The TL ratio was an independent prognostic factor for overall survival in CRC. However, there was no significant correlation between TL ratio and the disease-free survival rate.

Garcia-Aranda et al. explored 91 CRC tissue samples¹². They measured telomere length in CRC tissue samples and paired normal tissue samples. They also accessed telomerase activity and expression level of telomeric repeat-binding factor (TRF1), which is one of six subunits of the shelterin complex. Patients with longer telomeres showed a significantly shorter disease-free survival rate (p=0.02). Cox regression analysis also proved that telomere length was an independent prognostic factor (p=0.04). In patients with Dukes stage C tumors, both longer telomere length and higher TL ratio were significantly associated with shorter disease-free survival rate (p=0.03 and p=0.04, respectively). Additionally, patients with shortened telomeres expressed higher TRF1 levels than patients without telomere shortening. Furthermore, among patients with telomerase-positive tumors, lower TL ratio and TRF1 over-expression was associated with longer disease-free survival (p=0.03 and p=0.05, respectively).

Getler et al. analyzed telomere length and hTERT expression in 57 CRC tissue samples and adjacent normal tissue samples¹³. Patients with longer TL ratio showed a significantly shorter overall survival rate compared with patients with shorter TL ratio (p<0.002). In multivariate Cox regression analysis, TL ratio was an independent prognostic factor; longer TL ratio predicted shorter overall survival (p<0.03). Additionally, telomere length and hTERT expression correlated significantly in cancer tissues and normal tissues (p<0.001 and p<0.001, respectively), and telomere length was shorter in cancer tissue compared with normal mucosa (p<0.001). The authors suggested that hTERT-mediated telomere stabilization might play a role in the progression and prognosis of CRC.

Studies finding no association between telomere length and CRC prognosis

The following four studies did not prove an association between telomere length and prognosis of CRC^14,15–17. Bae et al. analyzed telomere length in 60 CRC tissue samples and corresponding nonmalignant normal tissue samples¹⁴. In the survival analysis, there was no association between telomere length and overall survival rate or disease-free survival rate. They also evaluated the expression level of telomeric repeat-containing RNA (TERRA) in cancer tissue and normal tissue. TERRA refers to a class of long noncoding RNAs which forms an integral component of telomeric heterochromatin²⁰. TERRA is also known to regulate telomere length and telomerase activity²¹. The analysis showed a significant association between TERRA expression and telomere length (p<0.05). However, it did not prove any statistical significance of TERRA as a prognostic factor for overall survival or disease-free survival although there was a tendency that survival was better in TERRA high group.

Suraweera et al. analyzed telomere length in 419 CRC tissues and adjacent normal tissues¹⁵. Telomere length was significantly shorter in cancer tissues than in normal tissues (p<0.001). Survival analysis was performed only in stage II and III CRC (n=281). There was no significant association between overall survival (n=281) or disease-free survival (n=246) and tumor length or TL ratio.

Lopez-Doriga et al. analyzed telomere length in cancer tissues and adjacent normal tissues from 42 patients with stage II colon cancer¹⁶. Significant shortening of telomere length was identified in cancer tissues as compared to their adjacent normal tissues (p<0.01). No significant relationship was observed between the recurrence rate and telomere length or TL ratio.

Kojima et al. measured telomere length, length of telomere 3’-overhang (3’-OH) and telomerase activity from 106 CRC tissue samples and corresponding noncancerous normal mucosa¹⁷. There was no significant association between telomere length and prognosis. However, patients with shortened 3’-OH showed a significantly increased survival rate compared with those without 3’-OH shortening among patients with telomerase-activated cancers, (p=0.018). Additionally, expression levels of telomere binding proteins (TBPs) were analyzed in cancer samples and normal mucosa samples. The analysis revealed all TBPs, except for protection of telomeres 1 (POT1), which is one of six subunits of the shelterin complex, were downregulated in cancers. In the telomerase-activated cancers, there was a significant correlation between the length of 3’-OH and expression level of POT1. The authors suggested that elongation of telomeric 3’-OH could increase malignant potential in CRC and that might be regulated by POT1.

Telomere length in peripheral leukocytes and CRC prognosis

Lastly, there were two studies analyzing telomere length in peripheral leukocytes from CRC patients^18,19. The two studies presented conflicting results. Chet et al. analyzed telomere length of peripheral leukocytes from 571 CRC patients, who were followed up for 28 months¹⁸. Patients with longer telomere length presented significantly longer overall survival and longer disease-free survival (p<0.001 and p<0.001).

Svenson et al. analyzed 130 blood samples of CRC patients and followed up the patients for 202 months¹⁹. On the contrary to the previous study, patients with shorter telomere length showed significantly longer overall survival (p=0.030).

Underlying data

All data underlying the results are available as part of the article and no additional source data are required.

Extended data

Figshare: review protocol.docx. https://doi.org/10.6084/m9.figshare.8075207.v1⁷.

Extended data are available under the terms of the Creative Commons Attribution 4.0 International license (CC-BY 4.0).

Reporting guidelines

PRISMA-ScR checklist for article “Telomere length as a prognostic marker in colorectal cancer: a scoping review”. https://doi.org/10.6084/m9.figshare.8072540.v1⁶.